desktop: save indicator bug

when having two unsaved documents open and pressing cmd+s, both documents loose the star in the titlebar.
I did not investigate if both get actually saved or if its a display bug.

Start by reproducing the report with two unsaved documents and pressing Cmd+S, then determine whether both documents are saved or only their title-bar indicators change. No file or test is named; the fix is complete when saving one document updates only the correct indicator and the other document's saved state remains accurate.

Written by the indexing model from the issue text.